Effects of aqueous Na/K and dietary K on growth and physiological characters of the Pacific white shrimp,Litopenaeus vannamei,reared in low‐salt well water

The synchronous effects of aqueous Na/K and dietary potassium (K⁺) on growth and physiological characters was studied on the Pacific white shrimp (Litopenaeus vannamei) reared in low‐salinity well water (4 ppt) for 8 weeks with initial weight of 0.28 ± 0.01 g. Three practical diets were formulated with supplement of 0, 0.3%, 0.6% K⁺ which contained 1.29 g/100 g, 1.60 g/100 g, 1.93 g/100 g K⁺ respectively. The supplement of K⁺ to the low‐salinity well water was 10, 20, 40 mg L^?1 which formed Na:K ratios of 42:1, 33:1, 23:1 respectively. Results showed that when the aqueous Na:K ratio was 42 and dietary K⁺ was 1.93 g/100 g K⁺, the WGR and PER of L. vannamei were the highest and the FCR was lower than that of others (P < 0.01). Supplement of K⁺ into well water and diets did not showed significant effects on haemolymph ammonia‐N, uric acid, urea content (P > 0.05), but had a extremely significant effect on arginase activity and Cl^? concentration (P < 0.01). Moreover, similar results were observed in alkaline phosphatase (ALP), bacteriolytic activity (LSZ) and respiratory burst activity (O₂^?) (P < 0.05). These results suggested that aqueous Na/K in the low‐salt well water and dietary K had significant synergistic effect on the growth, osmoregulation and immunity of L. vannamei. Concluded from the growth performance, nitrogen metabolism, osmoregulation and immunity, as the Na/K in the low‐salinity well water descended from 42 to 23, the requirement of dietary K⁺ was also decreased.     

Effects of dietary mannanase on growth,metabolism and non‐specific immunity of Tilapia (Oreochromis niloticus)

An experiment was designed to assess the effects of a commercial β‐mannanase on performance and immunity of tilapia fed plant‐based diets. A basal diet was supplemented with 0.0 (control), 0.5 and 1.0 g β‐mannase kg⁻¹ to formulate three experimental diets. Each treatment contained 4 tanks with 30 fish per tank. Trial lasted 8 weeks. Our results demonstrated that β‐mannanase addition (0.5 and 1.0 g kg⁻¹) improved significantly (P < 0.05) the final weight, specific growth rate (SGR), protein efficiency ratio (PER) and feed conversion ratio (FCR) compared with the control (0.0 g kg⁻¹). There were no significant differences in feed intake (FI) and survival rate (SR) among the 3 dietary treatments (P > 0.05). β‐mannanase supplementation also led to an increase (P < 0.05) in amylase, trypsin and Na⁺K⁺‐ATPase activities in intestine, and an decrease (P < 0.05) in aspartate transaminase (AST) and alanine transaminase (ALT) activities in serum compared with the control. However, dietary enzyme supplementation had no significant effect on the serum triacylglycerol (TG), cholesterol (CHO), high density lipoprotein cholesterol (HDL‐C), low density lipoprotein cholesterol (LDL‐C) and very low density lipoprotein cholesterol (VLDL‐C) (P > 0.05). Moreover, the dietary β‐mannanase supplementation groups exhibited an increase in the total leukocyte counts (WBC), differential leukocyte counts, respiratory burst activity, lysozyme activity and superoxide dismutase (SOD) activity compared to the controls (P < 0.05). In conclusion, β‐mannanase addition to tilapia diets improved feed utilization and non‐specific immunity resulting in improvements in growth performance.     

饲料中添加龙须菜对眼斑拟石首鱼生长、脂肪酸组成、免疫及肠道的影响

为了研究添加龙须菜(Gracilaria lemaneiformis)对眼斑拟石首鱼(Sciaenops ocellatus)生长、脂肪酸组成、免疫和肠道的影响,在饲料中分别添加0(对照组)、1%、2%、3%、4%和5%的龙须菜,饲养初始体质量(9.38±0.06)g的眼斑拟石首鱼8周。结果表明,添加龙须菜对鱼体成活率、增重率(WG)和特定生长率(SGR)均不存在显著性影响(P0.05),但1%~4%组的增重率均高于对照组,1%组的饲料效率和特定生长率最高;所有龙须菜添加组全鱼脂肪酸中的二十二碳六烯酸(DHA)均高于对照组,且添加量为5%时DHA显著高于对照组(P0.05);肝脏中超氧化物歧化酶(SOD)活性在4%组显著高于对照组(P0.05);3%组肠道黏膜褶最高且组织状况最好。由此可见,饲料中添加龙须菜对眼斑拟石首鱼生长有一定的促进作用,且添加适量龙须菜可以改善眼斑拟石首鱼的肝脏和肠道健康,提高全鱼DHA含量。     

嗜水气单胞菌菌蜕系统的构建及其免疫效果研究

【目的】探讨鱼源嗜水气单胞菌菌蜕系统的可行性和应用性。【方法】以PhiX174基因组DNA为模板,对LysisE基因进行PCR扩增,并将纯化的PCR产物与原核表达载体pBV220双酶切后连接,构建溶菌质粒pBV220-LysisE。将pBV220-LysisE转入嗜水气单胞菌LN0925株中,构建LN0925(pBV220-LysisE)菌蜕疫苗(AHGs),进而通过溶菌动力学过程检测、电镜下细菌形态观察和动物免疫保护试验等评价所制备的菌蜕疫苗。【结果】PCR扩增成功获得长度为276bp的噬菌体LysisE基因;成功构建pBV220-LysisE重组质粒及AHGs。在42℃诱导60min后,LN0925(pBV220-LysisE)菌株开始出现溶菌现象,至3h后溶菌基本结束;溶菌至210min时,其裂解效率达到99.99%。菌液浓度对菌蜕裂解效率的影响试验表明,不同浓度质粒pBV220-LysisE均可以高效诱导嗜水气单胞菌LN0925株裂解。电镜观察发现,AHGs形成明显的溶菌孔道,整体细胞形态完好,且内容物流失。动物免疫保护试验结果表明,AHGs疫苗能明显提高鲤鱼的血清抗体水平,在免疫后5-6周血清抗体凝集效价达到1∶256,从第7周开始呈下降趋势;AHGs和甲醛灭活疫苗(FKC)的相对保护率分别为77.78%和55.56%。【结论】AHGs能够有效激活鱼体的免疫系统并产生免疫保护,且较FKC具有更好的免疫保护效果。     

Natural history of Arabidopsis thaliana and oomycete symbioses

Molecular ecology of plant–microbe interactions has immediate significance for filling a gap in knowledge between the laboratory discipline of molecular biology and the largely theoretical discipline of evolutionary ecology. Somewhere in between lies conservation biology, aimed at protection of habitats and the diversity of species housed within them. A seemingly insignificant wildflower called Arabidopsis thaliana has an important contribution to make in this endeavour. It has already transformed botanical research with deepening understanding of molecular processes within the species and across the Plant Kingdom; and has begun to revolutionize plant breeding by providing an invaluable catalogue of gene sequences that can be used to design the most precise molecular markers attainable for marker-assisted selection of valued traits. This review describes how A. thaliana and two of its natural biotrophic parasites could be seminal as a model for exploring the biogeography and molecular ecology of plant–microbe interactions, and specifically, for testing hypotheses proposed from the geographic mosaic theory of co-evolution.     

鞭毛素蛋白FliCxcv对水稻免疫反应的诱导功能鉴定

 为揭示来源于番茄细菌性斑点病菌(Xanthomonas campestris pv. vesicatoria, Xcv)菌株XV18鞭毛素(FliCxcv)作为一种病原相关分子模式(PAMP)诱导水稻免疫反应的功能,本研究对FliCxcv编码基因flicxcv进行了基因克隆、序列分析、原核表达、蛋白纯化和诱导活性测定。结果表明,通过PCR特异性扩增,从Xcv菌株XV18中克隆了1 200 bp的fliCxcv基因片段,其序列与GenBank中己测序菌株的完全一致。在大肠杆菌中对该基因全长、N端和C端截短序列进行了原核表达,并获得了纯化的FliCxcv全长及其截短蛋白。将纯化蛋白浸润接种到水稻品种日本晴叶片组织,发现FliCxcv全长及其截短蛋白均能诱导水稻叶片细胞死亡、H₂O₂产生以及防卫基因(OsPAL和OsPR1b)表达等免疫反应,但诱导活性存在差异。因此,本研究验证了FliCxcv具有激发水稻细胞免疫反应的PAMP功能,为水稻免疫诱导制剂的研发提供了材料。     

Spectroscopic properties of humic acids isolated from the rhizosphere and bulk soil compartments and fractionated by size-exclusion chromatography

The humic acids (HAs) isolated by conventional procedure from rhizosphere (r) and bulk (c) soils were analyzed by means of chemical and physico-chemical techniques. Two different crops were selected, tomato (T) and artichoke (A), and each HA was fractionated by size-exclusion chromatography (SEC) into three fractions with increasing molecular size, respectively, Fraction I (FrI) < Fraction II (FrII) < Fraction III (FrIII). Elemental analysis data indicated greater N and S contents in the rhizosphere T-HAs, with respect to rhizosphere A-HA, which suggests the occurrence in the former ones of a large amount of organic nitrogen- and sulfur-containing compounds that are released by the rhizodeposition processes. Further, the three HA fractions from the bulk soils of the two series showed a gradual increase of C, H, and N contents, and a decrease of O and S contents and C/N and C/H ratios. These results suggested that the lowest molecular size fractions are richer in oxygenated functional groups, whereas the higher molecular size fractions are richer in N-containing groups and structural C- and H-containing units. The three HA fractions from the rhizosphere soils of the two series showed a gradual decrease in C content, and an increase of H, N, and O contents, which suggests the possible incorporation into soil HAs of a multitude of C-containing compounds of low molecular size released by plant roots. The FT-IR data, in general, suggested that the contents of carboxylic, phenolic and N-containing groups and polysaccharide-like components in HAs from rhizosphere soils are larger than those of HAs from the corresponding bulk soils. Further, the FrI fraction consisted mainly of simple structural units, likely quinonic and phenolic units with a prevalent aromatic character, whereas the FrII and, especially, FrIII fractions featured a mixed aliphatic/aromatic nature and a greater molecular complexity. The extent of these differences appeared to depend on the plant species and age, and is mainly due to the partial incorporation into rhizosphere HAs of typical root exudate components, such as amino acids, amides, aliphatic and aromatic acids of low molecular size, polysaccharides and sugars, fatty acids and sterols, and enzymes.     

Rapid quantification of Bacillus subtilis antibiotics in the rhizosphere

Biological control agents like Bacillus subtilis offer an alternative and supplement to synthetic pesticides. Antibiotic production by biocontrol strains of B. subtilis can play a major role in plant disease suppression. Our current understanding of B. subtilis antibiosis comes from culture media measurements of antibiotic production and in vitro suppression of pathogens. Quantifying the antibiotic metabolite chemistry of B. subtilis biofilms growing on root surfaces provides a more accurate understanding of in vivo antibiotic production. An analytical method based on solid-phase extraction (SPE) with high-performance liquid chromatography (HPLC) and mass spectroscopy (MS) has been developed to quantify antibiotics produced by B. subtilis growing on plant roots. Cucumber (Cucumis sativus) was grown in composted soil and potting media inoculated with B. subtilis strain QST 713 (AgraQuest, USA). Two important B. subtilis antibiotics, surfactin and iturin A, were extracted from root and rhizosphere soil using acidified organic solvents followed by cleaning and concentration using SPE. HPLC and HPLC-MS were used to measure surfactin and iturin A. Rhizosphere concentrations of both antibiotics increased with plant age. For plants grown in peat-based potting media, surfactin concentrations increased from 9 μg g⁻¹ root fresh weight (RFW) at 15 d to 30 μg g⁻¹ RFW at 43 d. Iturin concentrations were 7 μg g⁻¹ RFW at 15 d and 180 μg g⁻¹ RFW at 43 d. In an initial field trial in a composted fine sandy loam, we demonstrated rhizosphere production of surfactin and iturin under competition and predation by the myriad macro- and microfauna existing in a fertile high-organic soil, with mature B. subtilis-inoculated cucumber roots yielding 33 μg g⁻¹ RFW surfactin and 630 μg g⁻¹ RFW iturin at 78 d.     

A new mycorrhizal helper bacterium, <Emphasis Type="Italic">Ralstonia</Emphasis> species,in the ectomycorrhizal symbiosis between <Emphasis Type="Italic">Pinus thunbergii</Emphasis> and <Emphasis Type="Italic">Suillus granulatus</Emphasis>

In a Robinia-pseudoacacia-dominated coastal forest in Tottori prefecture Japan, the growth and survival of Pinus thunbergii seedlings and the natural regeneration of P. thunbergii was disturbed by R. pseudoacacia. In order to improve the growth of P. thunbergii seedling in the Tottori sand dune, we tried to find a mycorrhiza helper bacteria (MHB) from P. thunbergii mycorrhizosphere in a Tottori sand dune. Two MHB, Ralstonia sp. and Bacillus subtilis, were selected from the nine bacterial species isolated from the mycorrhizosphere of P. thunbergii. The bacterial effect on the ectomycorrhizal fungus Suillus granulatus was investigated by confrontation assay and a microcosm experiment. The confrontation assay showed that Ralstonia sp. promoted the hyphal growth of S. granulatus. Moreover, the S. granulatus–P. thunbergii symbiosis was significantly stimulated by Ralstonia sp. and B. subtilis. Ralstonia sp. and B. subtilis were regarded as MHB associated with P. thunbergii. This is the first report of Ralstonia sp. as an MHB.     

Selection for root colonising bacteria stimulating wheat growth in saline soils

High salinity of soils in arid and semi-arid regions results in desertification and decreased crop yield. One possibility to circumvent this problem is to use root colonising salt tolerant bacterial inoculants which can alleviate salt stress in plants. In the present work, the best five enhanced wheat root tip coloniser bacteria were selected from the rhizosphere of wheat grown in saline soil and were identified by the 16S rRNA gene sequence as Pseudomonas putida, Pseudomonas extremorientalis, Pseudomonas chlororaphis and Pseudomonas aurantiaca. The isolates tolerated salt of 5% NaCl and produced indole acetic acid under saline conditions. Four isolates proved to be very efficient in promoting a significant increase in the shoot, root and dry matter of wheat and were able to survive in saline soil. Four of the isolated strains appeared to be better competitive colonisers than reference strains and probably outcompeted with indigenous microorganisms of the rhizosphere. These results are promising for the application of selected environmentally save microbes in saline agricultural soils.